News: Meat-eating dinosaur from Argentina had bird-like breathing system.

Meat-eating dinosaur from Argentina had bird-like breathing system

http://www.eurekalert.org/pub_releases/2008-09/uom-mdf092608.php

ANN ARBOR, Mich.--The remains of a 30-foot-long predatory dinosaur
discovered along the banks of Argentina's Rio Colorado is helping to
unravel how birds evolved their unusual breathing system.

University of Michigan paleontologist Jeffrey Wilson was part of the
team that made the discovery, to be published Sept. 29 in the online
journal Public Library of Science ONE and announced at a news
conference in Mendoza, Argentina.

The discovery of this dinosaur builds on decades of paleontological
research indicating that birds evolved from dinosaurs.

Birds have a breathing system that is unique among land animals.
Instead of lungs that expand, birds have a system of bellows, or air
sacs, which help pump air through the lungs. This novel feature is the
reason birds can fly higher and faster than bats, which, like all
mammals, expand their lungs in a less efficient breathing process.

Wilson was a University of Chicago graduate student working with noted
dinosaur authority Paul Sereno on the 1996 expedition during which the
dinosaur, named Aerosteon riocoloradensis ("air bones from the Rio
Colorado") was found. Although the researchers were excited to find
such a complete skeleton, it took on even more importance as they
began to understand that its bones preserved hallmark features of a
bird-like respiratory system.

Arriving at that understanding took some time. Laboratory technicians
spent years cleaning and CT-scanning the bones, which were embedded in
hard rock, to finally reveal the evidence of air sacs within
Aerosteon's body cavity. Previously, paleontologists had found only
tantalizing evidence in the backbone, outside the cavity with the
lungs.

Wilson worked with Sereno and the rest of the team to scientifically
describe and interpret the find. The vertebrae, clavicles, and hip
bones bear small openings that lead into large, hollow spaces that
would have been lined with a thin layer of soft tissue and filled with
air in life. These chambers result from a process called
pneumatization, in which outpocketings of the lungs (air sacs) invade
the bones. Air-filled bones are the hallmark of the bellows system of
breathing in birds and also are found in sauropods, the long-necked,
long-tailed, plant-eating dinosaurs that Wilson studies.

"In sauropods, pneumaticity was key to the evolution of large body
size and long necks; in birds it was key to the evolution of a light
skeleton and flight," Wilson said. "The ancient history and
evolutionary path of this feature is full of surprising turns, the
explanations for which must account for their presence in a huge
predator like Aerosteon and herbivores like Diplodocus, as well as in
a chicken."

In the PLoS ONE paper, the team proposes three possible explanations
for the evolution of air sacs in dinosaurs: development of a more
efficient lung; reduction of upper body mass in tipsy two-legged
runners; and release of excess body heat.

Sereno, a National Geographic Explorer-in-Residence, said he is
especially intrigued by heat loss, given that Aerosteon was likely a
high-energy predator with feathers but without the sweat glands that
birds possess. At approximately 30 feet in length and weighing as much
as an elephant, Aerosteon might well have used an air system under the
skin to rid itself of unwanted heat.

###

In addition to Sereno and Wilson, coauthors of the PLoS ONE article
include Ricardo Martinez and Oscar Alcober of the Universidad Nacional
de San Juan, Argentina, David Varricchio of Montana State University
and Hans Larsson of McGill University. The expedition that led to the
discovery was supported by the National Geographic Society and The
David and Lucille Packard Foundation.

--
Bob.

.

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